1. Field of the Invention
The invention relates, on the one hand, to a linear drawing machine for the linear drawing of a workpiece through a drawing ring, a drawing unit, in which one or more drawing tools grasp the workpiece and draw it linearly in the drawing direction, being situated behind the drawing ring. On the other hand, the invention relates to a method for linear drawing of a workpiece through a drawing ring, a drawing unit being situated behind the drawing ring, which grasps the workpiece using one drawing tool or using multiple drawing tools and draws it linearly in a drawing direction.
2. Description of the Related Art
Linear drawing methods and linear drawing machines are primarily distinguished by differentiation from other drawing methods and drawing machines in that a force is applied linearly to the workpiece therein and is drawn through a drawing block and/or drawing ring, and are thus differentiated from drum drawing machines, for example, in which the traction force is applied in that the workpiece is laid around a drum, for example, in a V-shaped groove of a drum, and the drawing force is applied via a drum drive. Due to the latter measure, the workpiece deforms in its cross-section after the drawing, so that only limited requirements may be placed on the implementation of the cross-section in workpieces drawn in this way.
This is not the case in linear drawing methods and machines, in which only small changes of the cross-section caused by the drawing process are finally to be expected once the workpiece has passed the drawing ring.
Unequal distributions of the mass in the cross-section through the workpiece also result in practice after the drawing, which are caused in particular by unequal distributions already present in the undrawn workpiece. Unequal mass distributions of this type may be caused in this case, for example, by forging and/or rolling processes or local temperature differences during the production of a blank.
In particular in the drawing machining of tubular workpieces, one differentiates between fixed and floating drawing mandrels, the first being held on a rod or another very long holding device in front of the intake side at the height of the drawing ring, while the latter remains freely floating at the height of the drawing ring due to its shaping and the drawing movement, caused by an interaction between friction and displacement work. The interaction between friction and displacement work often ultimately results in axial oscillations, i.e., in oscillations along the drawing directions, which are also known in fixed drawing mandrels, however, in that the rod and/or the holding unit act as a spring at the lengths which are required, as described by Benson in his article “praktische and theoretische Gesichtpunkte bei der Gestaltung fliegender Ziehdorne [Practical and Theoretical Aspects in the Design of Flying Drawing Mandrels]” in der Zeitschrift für Metallkunde [The Magazine for Metallurgy], vol. 57, issue 10, October 1966 (1966-10) on pages 717 through 724.
While the axial oscillation is well controllable in particular in floating drawing mandrels by suitable design of a conical drawing mandrel part and a calibrating drawing mandrel part, these measures optionally also being able to be used in fixed drawing mandrels, unless they dispense with a conical drawing mandrel part entirely, there are various approaches for controlling the location of the drawing mandrel even perpendicular to the drawing direction, in order to improve the drawing result, in particular the uniformity in the cross-section of the workpiece to be drawn. If the rods or long holding units in fixed drawing mandrels are solely to be observed as long springs, it is immediately re-constructible that in this way a noticeable influence on the location of the drawing mandrel cannot also be performed perpendicular to the drawing direction, so that measures must also be used therein, precisely as with floating drawing mandrels, which engage in spatial proximity to the drawing ring. In this regard, a differentiation does not have to be made between fixed and floating drawing mandrels.
Thus, DE 196 10 642 A1 discloses a method and a device for the cold drawing of seamless tubes, in which the eccentricity and the inclination of the drawing mandrel relative to a drawing axis, an axis oriented parallel to the drawing direction and running centrally through the drawing ring, may be manipulated using a guide situated in the drawing direction behind the drawing ring and acting externally on the workpiece, in that the calibrating drawing mandrel part, which substantially defines the inclination of a drawing mandrel in any case, is lengthened up to the guide.
A manipulation possibility which is somewhat different, but nonetheless acts through a measure behind the drawing ring in the drawing direction, is disclosed in U.S. Pat. No. 3,167,176, in which the drawing mandrel, which exclusively comprises a calibrating part and is implemented fixed in this achievement of the object, is mounted behind the drawing ring so it is pivotable around a pivot point.
In addition, DE 196 10 642 A1 also discloses a displacement of the drawing ring, in order to be able to act correspondingly on the drawing result, U.S. Pat. No. 3,131,803 and DE 19 59 676 A also proposing an inclination change of the drawing ring.
EP 1 022 070 A2 also discloses a displaceable drawing ring and a mandrel guided opposite to the drawing direction, which can also be changed in regard to its inclination angle relative to the drawing axle by a force which can be applied on a mandrel guide located on the drawing mandrel opposite to the drawing direction. As is immediately obvious, in this design, the spacing between mandrel guide and drawing mandrel is selected as sufficiently small that a tilting torque can be transmitted effectively from the mandrel guide onto the mandrel, which is not possible with long rods or other long holding units, as are used in fixed drawing mandrels.
All of these measures substantially change the cross-section of the workpiece after the drawing and/or the mass distribution in the cross-section of the workpiece after the drawing and also in a predictable way. However, it has been shown that a uniform mass distribution can hardly be achieved using these measures, because complex changes in the mass distribution are caused by the inclination change of the drawing ring and/or the drawing mandrel, which possibly display the desired effects at one point, but necessarily cause a corresponding disadvantageous effect at another point. This is also true for eccentric displacements of the drawing ring or the drawing mandrel, for example, according to DE 196 10 642 A1, which also result in complex changes in the mass distribution of this type.